This invention relates generally to gas turbine engines and, more particularly, to gas turbine engine exhaust frames.
Gas turbine engines include a compressor for providing compressed air to a combustor wherein the air is mixed with fuel and ignited for generating combustion gases. The combustion gases are channeled to a turbine which extracts energy from the gases for powering the compressor and generating thrust to propel the aircraft. Because turbine flowpaths which channel the combustion gases are exposed to the hot combustion gases, thermal stresses may be induced therein. Continued exposure to the thermal stresses and hot combustion gases may cause radial thermal growth of the structures including increasing the diameter and circumference of the structures.
Gas turbine engines also include an annular frame. The frame includes a casing spaced radially outwardly from an annular hub. A plurality of circumferentially spaced-apart supports extend between the casing and the hub. The casing downstream of the combustor is exposed to hot combustion gases exiting the combustor. Accordingly, supports downstream from the combustor are also subjected to hot combustion gases.
Because the hub is more massive than the casing, and because much of the annular hub is not exposed to hot combustion gases, during transient turbine engine operations, operating temperatures of the casing increase much quicker than operating temperatures of the hub. As a result of such temperature differences, thermal stresses may develop between the hub and the casing. Continued exposure to thermal stresses may facilitate low-cycle fatigue cracking and eventual failure of the frame.
In an exemplary embodiment, a heat shield for a gas turbine engine hub reduces thermal stresses in an exhaust frame of the gas turbine engine. The hub is mounted within the engine with a plurality of supports that extend between the exhaust frame and the hub. The supports extend radially outward from the hub through a primary flow cavity and facilitate flow to a secondary flow cavity. The heat shield defines the secondary flow cavity such that the secondary flow cavity is radially inward and axially adjacent the hub. The heat shield includes a plurality of thermal stress relieving corrugations.
During operation, combustion gases flow from the primary flow cavity through the supports and into the secondary flow cavity defined by the heat shield. The combustion gases are retained adjacent the hub by the heat shield, and raise an operating temperature of the hub, thus facilitating a reduced temperature differential between the hub and the supports. Furthermore, the corrugations in the heat shield permit differential thermal expansion between the heat shield and the hub. As a result, thermal stresses between the supports, the hub, and the heat shield are facilitated to be reduced.